Evaporator apparatus



Feb. 14, 1967 H. H. NEWMAN EVAPORATOR APPARATUS Filed March 18, 1965 United States Patent O 3,303,870 EVAPGRATGR APPARATUS Hobart H. Newman, Palos Park, ill., assignor to Whiting Corporation, a corporation of Illinois Filed Mar. 1S, 1965, Ser. No. 440,740 6 Claims. (Cl. 159-27) The present invention relates to an improved forced circulation evaporation method and apparatus. More particularly, this invention concerns a novel circulating pump and heat exchanger arrangement for forced circulation evaporators wherein the heat exchanger is positioned upstream of the circulatinU pump. This construction results in substantially reduced erosive wear of the inlet ends of the heat transfer tubes in the heat exchanger and is particularly suitable for use in evaporator systems wherein slurries are circulated, such as, for example, in brine evaporators.

Conventional vertical tube evaporators having heat transfer tubes located within the evaporating chamber have generally used copper as the tube construction material because of its excellent thermal conducting properties. The use of this material in forced circulation evaporators, however, has not been completely satisfactory. In conventional forced circulation evaporators, a circulating pump and vheat exc-hanger are located outside the evaporating chamber and are arranged so that the circulating pump discharges into the heat exchanger forcing the liquid being circulated through the heat transfer tubes. It has been observed that when copper or copper alloy tubes are used in these heat exchangers, there is substantial erosive wear at the inlet ends of the heat transfer tubes. This erosive wear is particularly pronounced where slurries are circulated such as in the evaporation of brine, necessitating heat transfer tube replacement at relatively frequent intervals.

It is, therefore, an object of the present invention to provide a forced circulation evaporator apparatus which is free from erosive wear problems inherent in prior art forced circulation evaporators.

Another object of the present invention is to provide an improved forced circulation evaporator method and apparatus capable of operating for extended periods of time Without requiring heat exchanger tube replacement.

A further object of the present invention is to provide a pump and heat exchanger arrangement for forced circulation evaporators which substantially reduces the turbulence in the heat transfer tubes caused by the circulating pump, resulting in greatly prolonged heat transfer tube life.

A still further object of the present invention is to provide a forced circulation evaporator wherein the circulating pump is in direct communication with the evaporating chamber for substantially reducing the erosive effects of turbulence developed by the circulating pum-p on evaporator components which are prone to wear such as, for example, the heat exchanger tubes.

Another further object of the present invention is to provide a forced circulation evaporator wherein the circulating pump is positioned on the discharge side of the heat exchanger tubes so that the high degree of turbulence imparted to the liquid `being circulated is substantially reduced at the inlet side of the heat exchanger tubes.

A yet further object of the present invention is to provide a forced circulation evaporator wherein the dis- Patented Feb. 14, 1967 HCC charge end of the circulating pump communicates with the evaporating chamber through a conduit characterized by la low ow resistance so that the high degree of turbulence imparted to the liquid is dissipated with a minimum of wear to the evaporator components,

A still further object of the present invention is to provide a forced circulation evaporator wherein the circulating pump location permits the formation of a protective lm coating on the interior surfaces of the heat transfer tubes.

A still further object of the present invention is to provide a forced circulation evaporator wherein there is substantially uniform tluid fiow through each of the heat transfer tubes.

Other and further objects of the present invention will `become apparent from the following -detailed explanation of a preferred embodiment of the invention in connection with the accompanying drawing, wherein- FIGURE l is an elevational view, partially broken away in vertical section, of an evaporator installation embodying principles of the present invention;

FiGURE 2 is a -plan View of the evaporator shown in FIGURE l; and

FIGURE 3 is a fragmentary sectional view of one of the heat transfer tubes shown in the evaporator of FIGURE 1.

Referring to the drawing and, with particularreference to FIGURES 1 and 2, a single effect evaporator 11 is illustrated which includes an evaporating chamber 12, a heat exchanger 13 and circulating pump 14. The pump 14 is driven by a motor 15 and is connected on its discharge side 14a to the chamber 12 by means of a conduit 16. In order to `avoid cavitation, pump 14 should have a net positive suction head requirement equal to or less than the available static head minus the pressure drop loss through the suction piping and heater element.

As is best shown in FIGURE 1, evaporator body 12 has a main central elongated cylindrical body section 17 which is enclosed on its upper end by a tapered dome 18 and provided on its lower end with a frusto-conical section 19 from the bottom of which depends the usual solids removal leg 2d. A uidizing liquid or elutriating liquor is fed to the leg 2t? for facilitating removal of unwanted salt lumps thro-ugh outlet 25M. Produ-ct can be continuously withdrawn through discharge outlet 2Gb.

Feed stock to be evaporated is supplied to the evaporator through a feed inlet opening 22 in conduit 1o. The vapor is removed through an overhead outlet 23 in the dome 18 which can be connected with a condenser or other source of vacuum or reduced pressure. The products of evaporation (eg. salt crystals) settle in leg 2t) and are removed through opening Zibb for further treatment in accordance with techniques well known in the art. For example, in the evaporation of brine, a concentrated salt slurry collects in leg 2t) and is conventionally treated by pumping to settlers (not illustrated) from which the salt is drawn to centrifugals or lters and the liquid discharged to a feed tank where it is mixed with the fresh feed stock. it is to be understood, however, that the principles of the present invention are not dependent upon any particular products treatment.

Heat exchanger 13 is provided with a shell 25 having an inlet 26 formed therein through which the steam or other heating medium is introduced into the shell 25 in surrounding relation with heat exchanger tubes 27 which are supported between upper and lower header plates. Condensate drain a and vent connection 25b are provided at the lower end of shell 25. A conduit 28, extending from an outlet 29 formed in the frustoconical portion 19 of the chamber 12, directly connects the interior of the evaporting chamber with the inlet side of the heat transfer tubes 27 (i.e. above the upper header plate). The outlet side of the tubes (below the lower header plate) discharges into the suction side of centrifugal pump 14 by means of an elbow member 30. Inspection and removal of the tubes 27 is facilitated by means of manholes 31 and 32 and removable end cap 33.

Elbow member is supported by a rigid leg 34, and is also equipped with an expansion joint 35 which is interposed between the outlet of the heat exchanger 13 and the elbow member. A similar expansion joint 36 is provided at the discharge side 14a of the centrifugal pump 14.

Construction materials for heat exchanger 13 will, of course, vary in accordance with the materials being circulated and the heat transfer characteristics desired. In this connection, tubes 27 composed of a non-ferrous material such as, for example, copper and copper-nickel alloys have been employed in brine evaporating systems embodying the principles of the present invention without experiencing the excessive wear problems common with conventional forced circulation evaporators. It was originally believed that the excessive wear in the conventional forced circulation evaporators was due to the higher fluid velocity in the heat transfer tubes, however, applicant has discovered that this wear is apparently produced by high speed swirls and eddies developed by the centrifugal pump impellers. With the applicants novel construction the deleterious effects of these eddy currents and swirls are substantially reduced since they are completely dissipated in the low ow resistant conduit 16 and evaporating chamber 12. Thus, the superior heat transfer characteristics of copper and copper alloys are able to be employed in forced circulation evaporating systems constructed in accordance with the principles of the present invention without the previously encountered problem of repeated tube replacement.

In accordance with the present invention, the extended heat exchanger tube life is, in part, believed to be due to the formation of a protective layer on the tube inner surface 27a which acts to prevent erosion of the tubes. This protective layer comprises a monomolecular film and is not formed with conventional evaporating systems since the previously mentioned eddy currents and swirls imparted to the iluid by the centrifugal pump destroy the layer, leaving the interior tube surfaces exposed to the high speed turbulent ow.

In operation, the evaporator 11 is fed with a brine solution through the feed inlet 22 so that a liquid level of brine undergoing evaporation is maintained in the chamber 12 at a level approximately indicated by the dotted line 38, leaving a freeboard space 39 in the upper portion of the chamber 12. The brine is recycled through the evaporator system by passing from the outlet 29 through conduit 28 and into tubes (27 where it is heated by steam in the shell 25 of heat exchanger 13. After being heated, the brine enters elbow 30 and is pumped back to evaporating chamber 12 through conduit 16.

In past installations embodying this construction, it has been discovered that copper and copper alloy tubes showed only very minimal wear after prolonged periods of use wherein the conventional arrangements with the heat exchanger located on the discharge side of the pump would have necessitated a replacement. The significance of the present invention can be appreciated since it not only avoids the high cost of tube replacement but also results in much less costly down-time for replacing tubes and reduces operation expenses by the improved heat transfer obtained with copper and copper alloy tubes.

The major design -features of an installation made in accordance with FIG. 1 which would be capable of pro- 7 per square inch absolute.

ducing 163 tons per day of crystalline salt would be as follows:

The evaporator body 17 would have a diameter of 14 feet, the main cylindrical portion a height of 16 feet, the enclosed top 18 a height of 51/2 feet, the frusto-conical portion 19 a height of 11 feet, and the product removal leg 20 a height of 23 feet, and a diameter of 2 feet. The heat exchanger 13 would have an over-all height of 33 feet and would contain 931 heat exchanger tubes formed of -30 cupro-nickel each having an outside diameter of ll/i inches, and a length of 26 feet. The pump 14 would be rated at 1700 gallons per minute and be driven by a motor having horse power for pumping the fluid into the interior of evaporating chamber 12.

The net positive suction head requirement for the pump would be 20 feet. The static head, measured from the liquid level in the evaporating chamber to the center line of the pump would be 46 feet of slurry. The pressure drop through the suction piping would be equal to 61/2 feet of slurry. Accordingly, the available suction head of 391/2 feet of slurry would be greater than the requirement of the pump.

ln a typical operation the brine in the main body of the evaporator 11 would have a temperature of approximately 218 F. and a concentration of approximately 28.2 percent NaCl, and would carry approximately 25 percent by weight of suspended salt crystals. Brine would be withdrawn through the line 28 and recirculated through the heat exchanger 13 at a rate of 1700 gallons per minute with the brine being introduced into the conduit 16 at a concentration of approximately 26 percent and at a rate of 98 gallons per minute.

The steam or vapor in the freeboard space 36 would be at a temperature of 200 and at a pressure of 11.5 pounds The vapor would be withdrawn at a rate of 670 pounds per minute through the line 23. For certain installations, a compressor (not illustrated) could be employed to provide for discharge of the overhead product into the steam jacket 25.

While the illustrated embodiment has been of a singleeffect vertical-tube evaporation unit, it will be appreciated that the principles of the present invention apply equally well to multi-effect evaporating systems as well as to other types of forced-circulation evaporators, such as the horizontal heating arrangements commonly known in the art.

Although various minor modifications may be suggested by those versed in the art, it will be understood that I wish to embody within the scope of the patent warranted herein all such embodiments as properly come within the scope of my contribution to the art.

I claim:

1. In a forced circulation evaporator including an evaporating chamber having a recycle outlet and inlet formed therein, a mechanical pump and a heater having heat transfer tubes through which a liquid containing suspended solids is circulated, the improvement which comprises directly communicating said recycle outlet with the inlet of said heat transfer tubes, the outlet of said heat transfer tubes with the inlet of said mechanical pump and the outlet of said mechanical pump with said evaporating chamber inlet, whereby the erosive effect of said suspended solids on said heat transfer tubes is substantially reduced.

2. The forced circulation evaporator of claim 1 wherein said mechanical pump is a centrifugal pump.

3. The forced circulation evaporator of claim 2 wherein said suspended solids are sodium chloride crystals.

4. In the method of treating a body of feed material in a forced circulation evaporator which includes an evaporating chamber, a mechanical pump and a heater equipped with heat transfer tubes through which a liquid containing suspended solids is circulated, the improvement for minimizing erosive wear on said heat transfer tubes caused by said circulating suspended solids which comprises the step of discharging the flow of said liquid and suspended solids from said mechanical pump directly into said evaporating chamber, the flow from said evaporating chamber directly into said heat transfer tubes and the ow from said heat transfer tubes directly into said pump inlet, whereby erosive flow characteristics imparted to said circulating suspended solids by said mechanical pump are substantially dissipated in said evaporating chamber prior to reaching said heat transfer tubes.

5. The method of claim 4 wherein said mechanical pump is a centrifugal pump.

6. The method of claim 5 wherein said suspended solids are sodium chloride crystals.

References Cited by the Examiner UNITED STATES PATENTS 5/1929 Jeremiassen 23-301 5/1932 Jeremiassen 159-45 X 7/1934 Lowry 159-27 X 10/1956 Boyer 159-27 X 1/1963 Janovtchik 159--27 X FOREIGN PATENTS 6/1954 Great Britain.

NORMAN YUDKOFF, Primary Examiner.

I. SOFER, Assistant Examiner. 

1. IN A FORCED CIRCULATION EVAPORATOR INCLUDING AN EVAPORATING CHAMBER HAVING A RECYCLE OUTLET AND INLET FORMED THEREIN, A MECHANICAL PUMP AND A HEATER HAVING HEAT TRANSFER TUBES THROUGH WHICH A LIQUID CONTAINING SUSPENDED SOLIDS IS CIRCULATED, THE IMPROVEMENT WHICH COMPRISES DIRECTLY COMMUNICATING SAID RECYCLE OUTLET WITH THE INLET OF SAID HEAT TRANSFER TUBES, THE OUTLET OF SAID HEAT TRANSFER TUBES WITH THE INLET OF SAID MECHANICAL PUMP AND THE OUTLET OF SAID MECHANICAL PUMP WITH SAID EVAPORATING CHAMBER INLET, WHEREBY THE EROSIVE EFFECT OF SAID SUSPENDED SOLIDS ON SAID HEAT TRANSFER TUBES IS SUBSTANTIALLY REDUCED. 